Conventionally, when a film is formed on a glass substrate placed on a stage using a slit nozzle, there is known a detecting method for specifying foreign materials stuck to the surface of the stage and the back surface of the glass substrate (for example, see the patent reference 1). In the foreign material detecting method disclosed in the patent reference 1, on the slit nozzle, a glass substrate surface detecting sensor and a stage surface detecting sensor are provided, a clearance amount L1 between the leading end of the slit nozzle and glass substrate surface and a clearance amount L2 between the slit nozzle leading end and stage are measured, a difference between the two clearance amounts (L2−L1) is obtained, and the clearance amounts difference (L2−L1) is compared with the thickness of the glass substrate used, thereby checking the presence or absence of the distortion of the glass substrate caused by foreign materials stuck to the stage surface and glass substrate back surface, and thus specifying the foreign materials stuck to the stage surface and glass substrate back surface.
Also, since, when carrying out such glass substrate foreign material detecting method, the stage surface detecting sensor provided on the slit nozzle is able to monitor the state of the stage through the glass substrate and also monitor the flatness of the stage, the parallelism of the slit nozzle and stage can be maintained and the formation of a uniform film is possible.